JPS60259759A - Egr controller for diesel engine - Google Patents

Abstract

PURPOSE:To assure good exhaust performance even on a highland by providing means for comparing between the referential load corresponding with the rotation speed and the engine load and means for correcting EGR control command under low atmospheric pressure. CONSTITUTION:A throttle valve 6 and an EGR control valve 7 are arranged respectively in the intake path and EGR path. Means 21 for operating the target EGR rate on the basis of the detected levels from a load sensor 18 and a rotation sensor 19 and means 22 for controlling the openings of the throttle valve 6 and the EGR control valve 7 with correspondence to EGR control command are provided. While means 24 for operating the referential load corresponding with the rotation speed on the basis of the detected value from an atmospheric pressure detecting means 23 and means 25 for comparing said referential load with the engine load are provided. Furthermore means 26 for correcting the EGR control command under low atmospheric pressure with correspondence to the comparison results is provided. In such a manner, good exhaust performance can be assured even on a high land.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to an exhaust gas recirculation control device for a diesel engine.

(Prior art) Exhaust recirculation device (which recirculates part of the exhaust gas into the intake air to suppress combustion in order to reduce NOx emitted from the engine)
In order to improve the exhaust composition without impairing engine drivability, the flow rate of the recirculated exhaust gas (EGR gas) must be adjusted appropriately according to the operating conditions. need to be controlled.

Figure 7 shows an example of an exhaust recirculation control device installed in a conventional diesel engine (1981 DATSUN-810 Diesel Service Manual...Nippon i Motors ■198
1 is the air cleaner, 2 is the intake passage, 3 is the engine body, 4 is the exhaust passage, 5 is the intake passage 2
The intake passage 2 is provided with a throttle valve 6 on the upstream side of the opening of the EGR passage 5, and an EGR control valve 7 is provided in the middle of the EGR passage 5. equipped.

The throttle valve 6 is driven by a diaphragm device 8, and a negative pressure source (vacuum pump,
When negative pressure from a vacuum tank, etc.) 10 is applied, the chamber is placed in a predetermined half-open position, and when the pressure chamber 9 is exposed to the atmosphere, it is placed in a fully open position. Switching between negative pressure and atmospheric pressure at this time is performed via a three-way solenoid valve 12 that responds to a signal from a control circuit 11.

The EGR control valve 7 is driven by the second diaphragm device 13, and when the negative pressure from the negative pressure source 10 directly acts on the pressure chamber 14, it is in the fully open position, and when the negative pressure is reduced (by the orifice 15), it is in the half open position. When the pressure chamber 14 is opened to the atmosphere in the fully closed position. The switching between negative pressure, reduced pressure, and atmospheric pressure at this time is performed by second and third three-way solenoid valves 16 and 17 that respond to signals from the control circuit 11. However, three-way solenoid valves 12, 16, and 17 are blank when energized respectively)
/ and m are connected, and when the power is turned off, boats l and n are connected.

The control circuit 11 detects the engine load condition via a load sensor 18 that follows a control lever of a fuel injection pump (not shown), the engine rotation speed via a rotation sensor 19, and the engine rotation speed via a water temperature sensor 20. Detects the cooling water temperature, etc., and adjusts the EG according to the operating condition.
The three-way solenoid valve 12,
Drive 16°17.

For example, in a low load range where a relatively high rate of exhaust gas recirculation is required, the throttle valve 6 is controlled to be in a half-open position and the EGR control valve 7 is in a fully open position. A sufficient amount of EGR gas is refluxed by the negative pressure generated.

In the partial load range, the throttle valve 6 is set to the fully open position from this state to cancel the generation of suction negative pressure, and when the load increases to a certain extent, the EGR control valve 7 is set to the half open position to reduce the amount of EGR gas.

Furthermore, in a high load range where the load is large, the EGR control valve 7 is fully closed to stop exhaust gas recirculation so as to maintain a high output of the engine.

3- Also, when starting the engine or warming up the engine, in order to maintain good startability and promote warm-up, the EGR control valve 7 is fully opened.

In this way, appropriate exhaust gas recirculation is performed depending on the operating state of the engine.

However, even if exhaust recirculation is controlled in this way,
For example, when an engine is operated at high altitudes with low atmospheric pressure, the air density decreases and the weight of the air intake into the engine decreases, which increases the amount of fuel supplied and increases EGR.
The amount of gas will also increase. Therefore, at high altitudes, NOx
Although it is well reduced, the combustion condition tends to deteriorate, which causes the problem of smoke and particulate emissions.

(Object of the Invention) The present invention was made in view of these problems, and aims to ensure good exhaust performance even at high altitudes.

(Disclosure of the Invention) As shown in FIG. an EGR control valve 7 interposed in the middle of an EGR passage communicating with the engine; means 18 and 19 for detecting engine load and rotational speed; and means 21 for calculating a target EGR rate based on these detected values; This goal EG
In an exhaust gas recirculation control device for a diesel engine, which includes means 22 for calculating a JEGR control command value from the R rate and controlling the opening degrees of the throttle valve 6 and the EGR control valve 7 according to this command value, the atmospheric pressure means 23 for detecting, means 24 for calculating a reference load for the rotational speed from this detected value, and means 2 for comparing this reference load with the engine load.
5, and according to this comparison result, when the atmospheric pressure is low, the above E
Means 26 for correcting the GR control command value is provided.

Therefore, exhaust gas recirculation does not become excessive at high altitudes, etc., and therefore, it is possible to efficiently reduce NOx while preventing the generation of smoke and the like.

(Embodiment) FIG. 2 shows an embodiment of the present invention in the form of a flowchart, the mechanical configuration of which is the same as that of FIGS. 7 and 7, and the functional configuration of which is the same as that of FIG. 1.

First, at 101 and 102, the engine load 91 rotation speed N is detected from the load detection means (low dog sensor) 18, rotation speed detection means (rotation sensor) 19, and cooling water temperature detection means (not shown in FIG. 1) 20. , cooling water temperature T is the target EG
The R rate calculation means 21 includes an atmospheric pressure detection means (pressure sensor) 2.
The atmospheric pressure P from 3 is read into the reference load calculation means 24 VL:.

When the cooling water temperature T is lower than the lower limit temperature To, the process goes from 103 to 118, and the control means 22 follows the EGR control command value Sd (described later) so as not to recirculate the exhaust gas.

104 when the cooling water temperature T is higher than the lower limit temperature TO.
105, the calculation means 21 calculates the target EG set from the engine load Q and rotational speed N as shown in FIG.
The R rate (MEGR) is selected, and the MEGR control means 22 calculates an EGR control command value.

At this time, if the atmospheric pressure P is equal to or higher than a predetermined value p+ (for example, 1 atm), the process goes to 135, bypassing the correction routine described later from 106, and adjusting the throttle valve 6 and the EGR control valve according to the EGR control command value. The opening degree of valve 7 is controlled, and in this case, the MEGR is used to control valves 6 and 7 to be switched in stages to four stages A, B, C, and D as shown in FIG. .

For example, when MEGR is in a high rate range (zone C in Figure 3), the EGR control command value Sa is set so that valves 6 and 7 are in the A stage.
is selected, and in middle-level positions (B zone), valves 6 and 7 are in the B stage, in low-rate areas (C zone), valves 6 and 7 are in the C stage, and in O-level positions (d zone). valve 6,
EGR control command values Sb, S so that 7 becomes the D stage.
c, Sd are selected.

Then, at 135, a control signal corresponding to the EGR control command values Sa to Sd is output to the three-way solenoid valves 12, 16 and 17 to control the opening degrees of the throttle valve 6 and the EGR control valve 7.

On the other hand, the atmospheric pressure P is lower limit P which is lower than the predetermined value P1.

When the height is high, it is 106,107 to 108°109
．． 110, and at this time, if the MEGR is in the d zone, it is 135, and if it is in the C zone, it is in 111 to 118, b.
119-126 for zone, 1 for C zone
Enter the flow from 27 to 134.

However, atmospheric pressure P is the lower limit value P. When the temperature is too low, the above-mentioned cooling water temperature T is the lower limit temperature T. Just like when it's low,
Go from 107 to 118.

At 111.119 and 127, the reference loads Qco and Qbos Qao for the rotational speeds N of zones c, b, and C are read out in advance by the reference load calculating means 24, and 112
．． 120.128, from atmospheric pressure P to reference load Qco,
Load correction amounts Da, Db, and Da shown in FIG. 5 are selected corresponding to Qbo and Qao.

Reference load Qco I Qb at 113.121.129
The load correction amounts Da, Db, Da are subtracted from o +Qao, and the reference loads Qc, Qb, Qa after the subtraction and the engine load Q are determined by the comparison means 25 to be 114, 122.
It is compared at ゜130.

An example of the reference loads and load correction amounts at the rotational speed N in Figure 6 shows that the lower the atmospheric pressure P is, the lower the reference loads Qc, Qb, and Qa are, reducing the range of each zone. It is becoming narrower.

If the comparison result ΔQ is positive at 115.123.131, the EGR control command value S corresponding to each zone
c, Sb, and Sa are selected as they are, and 116.11
Go from 7, 124/125, 132/133 to 135.

On the other hand, if the comparison result △Q is negative, then 118°12
6.134, the EGR control command values Sc, Sb, and Sa are changed to Sd, Sc, and Sb by the correction means 26.

As mentioned above, the control signal corresponding to the EGR control command value S a - S d is output at 135.
Note that these Sa to Sd are stored in step 136 as the previous EGR control command value. In addition, H in Figure 2 is a hysteresis provided to maintain control stability, and the EGR control command value S a - S d is not switched unless the comparison result △Q becomes greater than the hysteresis H. .

Due to this configuration, the atmospheric pressure P is the lower limit value P. When the temperature is lower than that, the throttle valve 6 and the EGR control valve 7 are set to the opening degree of the D stage shown in FIG. 4, so that exhaust gas recirculation is not performed at extremely high altitudes where the air density is extremely low. Also, the cooling water temperature T is the lower limit value T. The same is true when warming up at a temperature lower than .

On the other hand, the cooling water temperature T is T. When the atmospheric pressure P is higher than 1 atm, the target EGR rate is selected based on the engine load Q and rotational speed N, and the stage corresponding to the target EGR rate (
The opening degrees of the throttle valve 6 and the EGR control valve 7 are controlled so as to achieve the following (see FIG. 4). Therefore, appropriate exhaust gas recirculation is performed in lowlands depending on the operating state of the engine.

On the other hand, the cooling water temperature T is T. The atmospheric pressure P is higher than P. When <P≦1, each zone (
The reference load (see FIG. 3) is modified, that is, the lower the atmospheric pressure P is, the narrower the ranges of zones a, b, and C are. Then, the reference load and the engine load Q at that time are compared, and when the engine load Q is out of the C zone, it is in the b zone, and when it is out of the b zone, it is in the C zone.
The opening degrees of the throttle valve 6 and the EGR control valve 7 are controlled so that when the vehicle deviates from the C zone, it switches to the D zone.

Therefore, when the atmospheric pressure P is low, exhaust gas recirculation is performed at a lower EGR rate, and therefore, exhaust gas recirculation does not become excessive at high altitudes where air density is low.

As a result, a good combustion state of the engine can be maintained even at high altitudes, NOx can be accurately reduced, and the generation of smoke and particulates can be sufficiently prevented.

Although the valves 6 and 7 are controlled in four stages in this embodiment, the opening degree may be controlled more finely or linearly.
In this way, more accurate exhaust gas recirculation control can be obtained.

(Effects of the Invention) In highlands where atmospheric pressure is low, NOx can be reduced while preventing the generation of smoke, etc., and there is an effect that exhaust performance 11- is further improved.

[Brief explanation of the drawing]

Fig. 1 is a diagram corresponding to complaints, Fig. 2 is a flowchart showing an embodiment of the present invention, Fig. 3 is a graph showing an example of setting the target EGR rate with respect to engine load and rotation speed, and Fig. 4 is a control operation for each stator. Figure 5 is a graph showing an example of setting the standard load correction amount, Figure 6 is a graph showing an example of setting the standard load correction amount, and Figure 6 is a graph showing an example of setting the standard load correction amount.
A graph showing an example, and FIG. 7 is a sectional view of a conventional example. 2...Intake passage, 4...Exhaust passage, 5...EGR
Passage, 6... Throttle valve, 7... EGR control valve, 12,
16゜17...Three-way solenoid valve, 18...Load sensor,
19... Rotation sensor, 20... Water temperature sensor, 21.
...Target EGR rate calculation means, 22...Control means, 23
...Atmospheric pressure detection means, 24...Reference load calculation means,
25... Comparison means, 26... Correction means. Patent Applicant: Nissan Motor Co., Ltd. 12- -400- Kata I Kenkawafu

Claims (1)

[Claims] A throttle valve installed in the middle of the intake passage, an EGR passage that connects the intake passage and the exhaust passage on the downstream side of the throttle valve, and an EGR control valve installed in the middle of the EGR passage. a means for detecting the load and rotational speed of the engine; a means for calculating a target EGR rate based on these detected values; and a means for calculating the target EGR rate plus an EGR control command value, In the exhaust gas recirculation control device for a diesel engine, which includes the throttle valve and means for controlling the opening degree of the EGR control valve, means for detecting atmospheric pressure, and means for calculating a reference load for the rotational speed from the detected value. and means for comparing the reference load and the engine load, and means for correcting the EGR control command value when atmospheric pressure is low according to the comparison result. Reflux control device.